Fumed Silanized Silica

ABSTRACT

Fumed silanized silica with the following physico-chemical data: Grindometer value less than 20 μm Tamped density 25 to 85 g/l is prepared by grinding fumed silica which has been silanized. It can be used in silicone rubber.

The invention relates to fumed silanized silica, to a process forpreparing it and to its use.

Fumed silica (pyrogenically prepared silicon dioxide) is known fromUllmanns Enzyklopädie der technischen Chemie, Volume 21, page 464(1982).

It is prepared by burning a vaporizable silicon compound, such assilicon tetrachloride, for example, in a mixture with hydrogen andoxygen.

The comminution of materials to form coarse powders (50-500 μm), finepowders (5-50 μm) and even greater finenesses (less than 5 μm) is commonand widespread practice. For all comminution tasks there is amultiplicity of technical and industrial equipment offered and operated,all adapted to the particular circumstances of the specific tasks. Agood overview of the comminution problems and of the diverse machines isgiven in Ullmanns Enzyklopädie der technischen Chemie, 3rd Edition,Volume 1, pages 616 to 638.

For fumed silica the average primary particle diameters are notablylower (5-50 nm) than can be obtained by mechanical comminution.

The primary particles and aggregates of the fumed silica with a surfacearea of 200 m²/g can be visualized in the electron microscope.

The primary particles and aggregates of a fumed silica agglomerate toform larger assemblies whose size is generally in inverse proportion tothe primary particle size or in proportion to the specific surface area.The agglomerate size also increases in line with the extent to which thefumed silica is compacted.

The binding forces holding these agglomerates together are relativelyweak. Nevertheless, when these agglomerates are incorporated into andbroken down in a liquid system for the purpose of homogeneousdistribution of the primary particles and aggregates, or particles witha low degree of agglomeration, a certain shearing energy is required.Depending on the particular field of application, dispersing is carriedout using any of a very wide variety of mixing devices, with determiningfactors for the selection being not only the viscosity and polarity ofthe system but also the agglomerate strength and the desiredhomogeneity.

With simple agitator mechanisms, such as paddle stirrers, it is usuallynot possible to carry out to satisfaction the direct incorporation ofsmall amounts of silicas, especially not when the systems in questionare of low viscosity. However, paint and varnish makers, and also thosewho carry out processing, have an interest in obtainingperformance-optimum distribution of the silicas, which are usedpredominantly as thickeners and thixotropic agents, by means of verysimple devices, with a very low energy input and in a very short time.

In the case of paddle-stirrer dispersing, the coarse silica agglomeratesare not sufficiently comminuted and hence are able to make only a smallcontribution to raising viscosities and thixotropy. The data relate to aUP resin (unsaturated polyester resin) as dispersion medium.

Reducing the agglomerate size by dispersing outside a liquid system, inother words, in practice, in the air, or by grinding in the conventionalsense, is possible only to a limited extent, since in the case ofmaterial with a given propensity to agglomerate the comminution isfollowed immediately by the re-establishment of the old agglomerationstate. This effect comes about no later than after recompaction of thematerial which as a result of the mechanical intervention has undergonea high degree of loosening and which in this form is not amenable todispatch and storage. The storage time as well would have the effect ofrenewed agglomerate enlargement.

A value taken as a dimensional number and evaluation variable for thestage of distribution of a dispersible silica and maximum agglomeratesize of the dispersion (granularity) is the so-called grindometer valueto DIN 53203.

A known procedure is to render fumed silica hydrophobic, to grind it ina pinned-disc mill and then to classify it (US 2004/0110077 A1).

This known silica is used as an external additive in toner mixtures.

Hydrophilic fumed silica with a BET surface area possesses a grindometervalue as determined in UP resin (unsaturated polyester resin Ludepal P6from BASF, 2% dispersion) in accordance with the DIN specification, of50 to 60.

If this fumed silica is also relatively highly compacted (100 to 120g/l), the grindometer value as well is also significantly higher,specifically more than 100, whereby necessitating an additional, notinconsiderable energy as a thickener and thixotropic agent.

A known procedure is to grind a highly dispersed silica having a surfacearea of approximately 300 m²/g in a pinned-disc mill.

The grindometer value achieved is initially, for the uncompacted silica,25.

If this silica is compacted to 50 g/l, the grindometer value rises to30, and in the case of further compaction to 75 g/l it rises to as faras about 40.

In the case of storage over a period of three months, the ground silica,not modified but compacted to 50 g/l, has a grindometer value of 50 to60.

Reagglomeration can only be prevented in accordance with the prior artif the hydrophilic silica is mixed with 3% by weight of a hydrophobicsilica and if this mixture is ground by means of an air-jet mill or apinned-disc mill (EP 0 076 377 B1).

In this case, for a fumed silica having a BET surface area of 200 m²/g,even after compaction to 73 or 107 g/l, a grindometer value of 35 isachieved.

For a fumed silica having a BET surface area of 300 m²/g, the additionof hydrophobic silica prior to grinding produces a grindometer value of10 for a tamped density of 28.1 g/l and of 15 to 20 for a tamped densityof 50 g/l.

The known fumed silicas have the disadvantage that they contain anunwanted fraction of hydrophobic silica.

The invention provides a fumed silanized silica which is characterizedin that it has the following physico-chemical data:

Grindometer value less than 20 μmTamped density 25 to 85 g/l

The invention further provides a process for preparing the silica of theinvention which is characterized in that silanized, structurallymodified fumed silicas which are characterized by groups fixed on thesurface, the groups being dimethylsilyl and/or monomethylsilyl,preferably dimethylsilyl, are ground.

In one preferred embodiment of the invention the silicas used can havethe following physicochemical data:

BET surface area m²/g: 25-400 Average primary particle size nm: 5-50 pH:3-10 Carbon content %: 0.1-10  

Fumed silicas are known from Winnacker-Küchler Chemische Technologie,Volume 3 (1983) 4th edition, page 77 and

Ullmanns Enzyklopädie der technischen Chemie, 4th edition (1982), Volume21, page 462.

Fumed silicas are prepared in particular by flame hydrolysis ofvaporizable silicon compounds, such as SiCl₄, for example, or organicsilicon compounds, such as trichloromethylsilane.

The silanized, fumed silicas used in accordance with the invention canbe prepared by treating fumed silica in a known way withdimethylchlorosilane and/or mono-methyltrichlorosilane, the groupsdimethylsilyl and/or monomethylsilyl being fixed on the surface of thefumed silica.

In one particular embodiment of the invention the initial silica usedcan be a fumed silicon dioxide which has been hydrophobicized by meansof dimethyldichlorosilane.

The grinding of the silanized fumed, silica can take place by means of apinned-disc mill or an air-jet mill.

The silica of the invention shows no propensity to reagglomerate. Thegrindometer value is below 20.

The fumed silica of the invention can be used as a filler in siliconerubber compounds.

Silicone rubber compounds and the use of fumed silica (AEROSIL®) insilicone rubber compounds are known (Ullmann's Encyclopaedia ofIndustrial Chemistry, Volume A 23, Rubber, 1, 221 ff.; Rubber 3, 3, 6ff.; Volume A 24, Silicones 57 ff. 1993).

Fumed silica is used on account of its excellent thickening effect(thixotroping) in silicone sealants, this thickening effect beingdesirable in the context of use as a jointing compound.

Where, however, the silicone rubber compounds are to be used as coatingmaterials, a low level of thickening is desired (U.S. Pat. No.6,268,300).

Of decisive importance in both cases is the optical quality of thesurface of the silicone vulcanizates.

It is an object of the present invention, therefore, to provide siliconerubber compounds which through the use of fumed silica as filler exhibitan optically high-grade surface after vulcanization.

The invention provides silicone rubber compounds containing 0.5% to 60%by weight, based on the total mass, of the fumed silica of the inventionhaving the following characteristic physicochemical data:

Grindometer value less than 20 Tamped density 25 to 85 g/land40% to 99.5% by weight, based on the total mass, of anorganopolysiloxane of the formula

Z_(n)SiR_(3-n)—O—[SiR₂O]_(x)—SiR_(3-n)-Z′_(n)

where R=alkenyl, alkoxy, aryl, oxime, acetoxy, alkyl radicals, having 1to 50 carbon atoms, unsubstituted or substituted by O, S, F, Cl, Br, I,in each case identical or different, and/or polystyrene, polyvinylacetate, polyacrylate, polymethacrylate and polyacrylonitrile radicalshaving 40-10 000 repeater units.

Z=OH, Cl, Br, acetoxy, amino, amineoxy, oxime, alkoxyamido, alkenyloxy,acryloxy or phosphate radicals, it being possible for the organicradicals to carry up to 20 carbon atoms, and in each case identical ordifferent.

Z′=oxime, alkoxy, acetoxy, amino, amido,n=1-3x=100-15 000.

As organopolysiloxane it is possible to use all polysiloxanes which haveor have been able to be used to date as a basis forroom-temperature-crosslinking (room-temperature-vulcanizing) (RTV)compositions. They may be described for example by the general formula

Z_(n)SiR_(3-n)—O—[SiR₂O]_(x)—SiR_(3-n)-Z′_(n)

where x, R, Z′ and Z have the following definitions:

where R=alkenyl, alkoxy, aryl, oxime, acetoxy, alkyl radicals, having 1to 50 carbon atoms, unsubstituted or substituted by O, S, F, Cl, Br, I,in each case identical or different, and/or polystyrene, polyvinylacetate, polyacrylate, polymethacrylate and polyacrylonitrile radicalshaving 40-10 000 repeater units.

Z=OH, Cl, Br, acetoxy, amino, amineoxy, oxime, alkoxyamido, alkenyloxy,acryloxy or phosphate radicals, it being possible for the organicradicals to carry up to 20 carbon atoms, and in each case identical ordifferent.

Z′=oxime, alkoxy, acetoxy, amino, amido,n=1-3x=100-15 000.

Within and/or along the siloxane chain in the formula indicated above itis also possible for there to be other siloxane units present, usuallyonly as impurities, in the form of diorganosiloxane units, for examplethose of the formula RSiO_(3/2), R₃O_(1/2) and SiO_(4/2), R in each casehaving the definition indicated for it above. The amount of these othersiloxane units ought not to exceed 10 mol percent.

Examples of R with the definition alkyl radical are, for example,methyl, ethyl, propyl, hexyl and octyl radicals; possible alkenylradicals are vinyl, allyl, ethylallyl and butadienyl radicals; and asaryl radicals it is possible to use phenyl and tolyl radical.

Examples of substituted hydrocarbon radicals R are in particularhalogenated hydrocarbon radicals such as 3,3,3-trifluoropropyl radical,chlorophenyl and bromotolyl radical; and cyanoalkyl radicals, such asthe β-cyanoethyl radical.

Examples of polymers as radical R are polystyrene, polyvinyl acetate,polyacrylate, polymethacrylate and polyacrylonitrile radicals which areattached to silicon via carbon.

On account of the greater ease of access the predominant fraction of theradicals R is composed of methyl groups. The other radicals R are, inparticular, vinyl and/or phenyl groups.

Particularly in the case of the presence of formulations which arestorable in the absence of water and which cure to elastomers at roomtemperature on ingress of water, Z and Z′ are hydrolysable groups.Examples of such groups are acetoxy, amino, amineoxy, alkenyloxy (forexample H₂C(CH₃CO—)), acyloxy and phosphate groups. Primarily on accountof the greater ease of access, preferred groups Z are acyloxy groups,especially acetoxy groups. Excellent results, however, are also achievedusing, for example, oxime groups, such as those of the formula—ON═C(CH₃)(C₂H₅), as Z. Examples of hydrolysable atoms Z are halogen andhydrogen atoms; examples of alkenyl groups Z are, in particular, vinylgroups.

The viscosity of the organopolysiloxanes used in the context of theinvention ought not to exceed 500 000 cP at 25° C., preferably 150 000cP at 25° C. Accordingly the value x ought preferably not to exceed 40000.

Examples of organopolysiloxanes which can be used are, for example, thesilicone polymers E50 (α,ω-hydroxydimethylsiloxypolydimethylsiloxane) orM50 (α,ω-hydroxydimethylsiloxypolydimethylsiloxane) from GE BayerSilicones.

Mixtures of different organopolysiloxanes can also be used.

The mixing of these organopolysiloxanes with the fumed silica and, whereappropriate, with the further constituents of the formulation of theinvention can take place in any desired known way, for example inmechanical mixing devices. It is accomplished very rapidly and easily,irrespective of the sequence in which the mixing constituents are added.

Preferably the fumed silicas of the invention are used in amounts of0.5% to 60% by weight, preferably 3% to 30% by weight, based on thetotal weight of the compounds which can be cured to elastomers.

If the only reactive terminal units present in the diorganopolysiloxaneswhich contain reactive terminal units are those having Si-bondedhydroxyl groups, then these diorganopolysiloxanes must be crosslinked.This can be done in a conventional way by means of the water present inthe air, with the addition where appropriate of further water, with acrosslinking agent. Here it is possible for example to use the Siloprencrosslinker 3034 from GE Bayer Silicones, the ethyltriacetoxysilaneoptionally in the presence of a condensation catalyst in a known way.Suitable catalysts for all formulations of the invention are, forexample, the Silopren catalysts DBTA or type 162 dibutyltin diacetate ordilaurate from the same manufacturer.

In one particular variant of the silicone rubber compounds of theinvention it is possible additionally for there to be 0.5%-20%,preferably 2%-10% by weight, based on the total weight of the compound,of a crosslinker having the formula

R′_(4-t)SiZ′₄

with R=alkyl, alkoxy, acetoxy, oxime, aryl, alkene radicals, having 1 to50 carbon atoms, unsubstituted or substituted by O, S, F, Cl, Br, I, ineach case identical or different, and/or polystyrene, polyvinyl acetate,polyacrylate, polymethacrylate and polyacrylonitrile radicals having5-5000 repeater units,

Z′=OH, Cl, Br, acetoxy, oxime, amino, amineoxy, alkenyloxy or phosphateradicals, it being possible for the organic radicals to carry up to 20carbon atoms, in each case identical or different, and

-   -   t=3 or 4.

All weight data relate to the total amount of silicone rubber compounds.

Examples of silanes of the formula indicated above areethyltriacetoxysilane, methyltriacetoxysilane,isopropyltriacetoxysilane, isopropoxytriacetoxysilane,vinyltriacetoxysilane, methyltrisdiethylaminooxysilane,methyltris(cyclohexylamino)silane, methyltris(diethylphosphato)silaneand methyltris(methylethylketoximo)silane.

Of course it is possible for formulations of the invention to contain,besides organopolysiloxanes, hydrophobicized silica, crosslinking agentsand crosslinking catalysts, if desired, fillers which are conventionallyused mostly or frequently in compounds which can be cured to elastomers.Examples of such substances are fillers having a surface area below 50m²/g, such as coarse quartz powder, kaolin, phyllosilicates, clayminerals, diatomaceous earth, additionally zirconium silicate andcalcium carbonate, and also untreated pyrogenically produced silicondioxide, organic resins, such as polyvinyl chloride powders,organopolysiloxane resins, fibrous fillers, such as asbestos, glassfibres and organic pigments, soluble dyes, fragrances, corrosioninhibitors, curing retardants, such as benzotriazole, and plasticizers,such as dimethylpolysiloxanes end-blocked by trimethylsiloxy groups.

Optionally the RTV 1K [one-component] silicone rubber compounds of theinvention can contain 0.1%-20%, preferably 0.1%-15%, with particularpreference 0.1%-10% by weight (based on the total amount of theformulation (of water-binding substances). Suitable substances for thispurpose are, for example, carboxylic anhydrides, for example aceticanhydride or maleic anhydride, and/or carbonic esters, such as forexample diethyl carbonate, ethyl carbonate and/or alkenyloxy compoundsand/or ketals, such as dimethyldioxolane, for example. It is possible touse one or more of these substances.

Additionally the silicone rubber compounds may contain 0.01% to 99.5% byweight of an unfunctionalized polysiloxane. Here it is possible to usethe polysiloxanes already specified, provided that they are notfunctionalized. One suitable, non-functional polysiloxane is, forexample, Baysilone oil M1000 (polydimethylsiloxane) from GE BayerSilicones.

Additionally the silicone rubber compounds may contain 0.01% to 6% byweight of organic or inorganic compounds of the metals Pt, Sn, Ti and/orZn as catalyst and/or 0.01% to 6% by weight of inhibitors and/or0.01%-6% by weight of fungicides and/or bactericides and/or 0.01% to 6%by weight of adhesion promoters (such as, for example, Silopren adhesionpromoter 3001 from GE Bayer Silicones, with the composition:di-tert-butoxydiacetoxysilane). As fungicides/bactericides it ispossible for example to use isothiazolinone, Vinycin orbenzisothiazolinone.

The silicone rubber compounds of the invention can be used as siliconerubber systems from the group of the room-temperature-vulcanizingone-component (1K RTV) silicone rubber sealants and also self-levellingroom-temperature-crosslinking silicone rubber compounds (1K RTV).

The silicone rubber compounds can be used as jointing compounds, windowsealants, seals in motor vehicles, sports equipment and householdappliances, heat-resistant seals, oil-exuding and chemical-resistantseals, and water-vapour-resistant seals, and seals in electrical andelectronic appliances.

The silicone rubber compounds can be used as coating materials fortextiles, e.g. lace tape (antislip), and textile materials, e.g. wovenglass fabric or woven nylon fabric.

The vulcanizates of the silicone rubber compounds of the inventionadvantageously have a high-grade surface.

The inventive examples were produced by metering commercial AEROSIL® R972 (bagged product) into the mill employed, using a metering balance,and subjecting it to grinding. The physicochemical data of theAEROSIL®972 are listed in Table 1.

The parameters of the production process are listed in Table 2.

The experiments were carried out using a pinned-disc mill (Alpine 160Z,rotor diameter 160 mm) or an air-jet mill (grinding chamber diameter:240 mm, grinding chamber height: 35 mm). The ground product was isolatedwith a hose filter (filter area: 3.6 m², filter material: woven nylonfabric). In further experiments the ground product obtained was packagedinto commercially customary bags using a commercially customary baggingmachine. In further experiments the bags packed with ground product wereleveled prior to palletization, using a method routine in the industryand suitable for the purpose.

TABLE 1 Fumed silica employed AEROSIL ® R 972 Attitude to waterhydrophobic Appearance white powder BET surface area¹⁾ m²/g  90-130Average primary particle size nm 16 Tamped density²⁾ g/l about 50 Losson drying³⁾ (2 h at 105° C.) % by <=0.5 weight on leaving supply plantLoss on ignition⁴⁾⁵⁾ % by weight <=2.0 (2 h at 1000° C.) C content % byweight 0.6-1.2 pH⁶⁾⁷⁾ 3.6-4.4 SiO₂ content⁸⁾ % by weight >=99.8 Al₂O₃content⁸⁾ % by weight <=0.050 Fe₂O₃ content⁸⁾ % by weight <=0.010 TiO₂content⁸⁾ % by weight <=0.030 HCl content⁸⁾⁹⁾ % by weight <=0.050 ¹⁾ToDIN ISO 9277 ²⁾To DIN EN ISO 787-11, JIS K 5101/20 (unsieved) ³⁾To DINEN ISO 787-2, ASTM D 280, JIS K 5101/23 ⁴⁾To DIN EN 3262-20, ASTM D1208, JIS K 5101/24 ⁵⁾Based on the substance dried at 105° C. for 2hours ⁶⁾To DIN EN ISO 787-9, ASTM D 1208, JIS K 5101/26 ⁷⁾Water:methanol= 1:1 ⁸⁾Based on the substance calcined at 1000° C. for 2 hours ⁹⁾HClcontent in constituent from loss on ignition

TABLE 2 Preparation of the inventive example parameters GA** GA** IA***IA*** quantity pressure quantity pressure Metering Designation Mill*[m³] [bar] [m³] [bar] [kg/h] Bagging Levelling Example 1 AJ 11.8 1.0 6.81.2 10 no no Example 2 AJ 11.8 1.0 6.8 1.2 10 yes no Example 3 AJ 11.81.0 6.8 1.2 10 yes yes Example 4 AJ 27.3 3.5 15.8 3.7 10 no no Example 5AJ 27.3 3.5 15.8 3.7 10 yes no Example 6 AJ 27.3 3.5 15.8 3.7 10 yes yesExample 7 PD — — — — 10 no no Example 8 PD — — — — 10 yes no Example 9PD — — — — 10 yes yes Example 10 PD — — — — 20 no no Example 11 PD — — —— 20 yes no Example 12 PD — — — — 20 yes yes AJ* = Air-jet mill PD =Pinned-disc mill GA** = Grinding air IA*** = Injector air

TABLE 3 Physicochemical data of the inventive silicas and thecomparative example BET specific Tamped Grindometer surface area densityvalue Designation [m²/g] pH [g/l] [μm] Comparative 103 4.2 71 45 ExampleExample 1 102 4.2 27 <20 Example 2 103 4.1 77 <20 Example 3 104 4.0 81<20 Example 4 103 4.2 31 <20 Example 5 104 4.2 58 <20 Example 6 103 4.280 <20 Example 7 103 4.2 31 <20 Example 8 104 4.2 72 <20 Example 9 1054.2 71 <20 Example 10 104 4.2 28 <20 Example 11 104 4.2 75 <20 Example12 104 4.2 70 <20

With virtually the same specific surface areas and unchanged pH values,the data of the ground products exhibit lower grindometer values.Surprisingly the lower grindometer values are retained in spite of thecompaction, evident through the tamped density, as a result of baggingor bagging/levelling.

In some cases the tamped densities are in fact above that of the oxideused, i.e. the oxides of the invention, despite the same or even highercompaction, exhibit lower grindometer values.

TABLE 4 Particle size determination by evaluation of TEM micrographs D50(g) Total span Designation DA [nm] DV [nm] [nm] [nm] Comparative 32.45841.608 38.466 3.420-90.82  example Example 1 23.532 26.673 25.7463.420-45.740 Example 4 25.680 34.157 27.306 2.500-70.580 Example 729.670 39.071 34.679 4.340-82.540 Example 10 29.491 39.810 33.8644.340-87.140 DA = Particle diameter, averaged over surface area DV =Particle diameter, averaged over volume D50 (g) = Median value, weightdistribution

The inventive fumed silica can have a D50 (g) (i.e. median value, weightdistribution) of 25.7 to 35.0 nm.

The total span of the particles can be 2500 to 87.140 nm.

The particle diameter averaged over the surface area, DA, can be 23.0 to30.9 nm.

The particle diameter averaged over the volume, DV, can be 26.5 to 40.0nm.

FIGS. 1 to 8 show the graphical representation of the distributions,measured on the silicas of Example 1 (in accordance with the invention)and of the comparative example.

TABLE 5 Particle size determination by Cilas Designation d50 value [μm]Comparative example 46.75 Example 1 6.95 Example 2 6.54 Example 3 6.61Example 4 4.57 Example 7 5.11 Example 9 6.34 Example 10 6.5 Example 116.36 Example 12 6.5

The silica of the invention can have a d50 value as determined by Cilasof 4.5 to 7.0 μm.

BET Surface Area

The BET surface area is determined in accordance with DIN ISO 9277.

Tamped Density

The tamped density is determined in accordance with DIN EN ISO 787-11.

Principles of Tamped Density Determination:

The tamped density (formerly tamped volume) is equal to the ratio of themass to the volume of the powder after tamping in a tamping volumeterunder defined conditions. According to DIN ISO 787/XI the tamped densityis reported in g/cm³. Owing to the very low tamped density of theoxides, however, we state the value in g/l. Furthermore, the drying andsieving, and the repetition of the tamping process, are omitted.

Apparatus for Tamped Density Determination:

Tamping volumeterMeasuring cylinderLaboratory balance (reading accuracy 0.01 g)

Tamped Density Determination Procedure:

200±10 ml of oxide are introduced into the measuring cylinder of thetamping volumeter so that there are no cavities remaining and so thatthe surface is horizontal.

The mass of the sample introduced is determined to an accuracy of 0.01g. The measuring cylinder containing the sample is inserted into thecylinder holder of the tamping volumeter and tamped 1250 times.

The volume of the tamped oxide is read off to an accuracy of 1 ml.

Evaluation of Tamped Density Determination:

${{Tamped}\mspace{14mu} {density}\mspace{14mu} \left( {g\text{/}l} \right)} = \frac{g\mspace{14mu} {initial}\mspace{14mu} {mass} \times 1000}{{ml}\mspace{14mu} {volume}\mspace{14mu} {read}\mspace{14mu} {off}}$

pH

Reagents for pH Determination:

Distilled or deionized water, pH>5.5

Methanol, p.a.

Buffer solutions pH 7.00 pH 4.66

Apparatus for pH Determination:

Laboratory balance (reading accuracy 0.1 g)Glass beaker, 250 mlMagnetic stirrerMagnetic rod, length 4 cmCombined pH electrodepH meter

Dispensette, 100 ml Procedure for Determining pH:

The determination takes place in a modification of DIN EN ISO 787-9.

Calibration: Prior to pH measurement the meter is calibrated using thebuffer solutions. Where two or more measurements are carried out oneafter another, a single calibration is sufficient.

4 g of oxide are pasted in a 250 ml glass beaker with 48 g (61 ml) ofmethanol and the suspension is diluted with 48 g (48 ml) of water andstirred for five minutes, with a pH electrode immersed, using a magneticstirrer (speed about 1000 min⁻¹).

After the stirrer has been switched off the pH is read off after astanding time of one minute. The result is reported to one decimalplace.

Grindometer Value Principles:

The degree of dispersion determines the performance properties of theliquid thickened with Aerosil. The measurement of the grindometer valueserves to assess the degree of dispersion. By the grindometer value ismeant the boundary layer thickness below which the particles oraggregates present become visible on the surface of the sample which hasbeen coated out.

The sample is coated out in a groove with a scraper, the depth of thegroove at one end being twice the size of the diameter of the largestAerosil particles, and decreasing steadily down to 0 at the other end.On a scale indicating the depth of the groove, the depth value is readoff, in micrometers, the value in question being that below which arelatively large number of Aerosil particles becomes visible as a resultof bits or scratches on the surface of the binder system. The value readoff is the grindometer value of the system present.

Apparatus and Reagents:

Hegmann grindometer with a depth range of 100-0 micrometer.

Polyester resin dispersion with 2% Aerosil, prepared according toTesting Instructions 0380.

Procedure:

The grindometer block is placed on a flat, slip-proof surface and iswiped clean immediately prior to testing. The Aerosil dispersion, whichmust be free from air bubbles, is then applied to the deepest point ofthe groove in such a way that it flows off somewhat over the edge of thegroove. The scraper is then held by both hands and placed,perpendicularly to the grindometer block and at right angles to itslongitudinal edges, with gentle pressure, onto the end of the groove inwhich the dispersion is located. The dispersion is then coated out inthe groove by slow, uniform drawing of the scraper over the block. Thegrindometer value is read off no later than 3 seconds after thedispersion has been coated out.

The surface of the spread dispersion (transverse to the groove) isviewed obliquely from above at an angle of 20-30° (to the surface). Theblock is held to the light in such a way that the surface structure ofthe spread dispersion is readily apparent.

The grindometer value read off on the scale is the value in micrometersbelow which a relatively large number of Aerosil particles becomevisible as bits or scratches on the surface. Individual bits orscratches occurring randomly are not taken into account in this context.

The granularity is assessed at least twice, in each case on a newlyspread dispersion.

Evaluation:

From the measured values the arithmetic mean is formed. The relationshipbetween the grindometer value in micrometers and the FSPT units andHegmann units, which are based on the inch system, is as follows:

B=8-0.079 A C=10-0.098 A=1.25 B

In this relationship:

A=Grindometer value in micrometersB=Grindometer value in Hegmann unitsC=Grindometer value in FSPT units

II. Preparation of Silicone Rubber Compounds 1. General ExperimentalProcedure

a) Principles

-   -   In order to test the performance properties of AEROSIL® in RTV1        silicone sealants, corresponding silicone compounds are prepared        on the laboratory scale to a standard formulation.

b) Apparatus

-   -   The planetary dissolver must meet the following requirements:    -   The stirring vessel has a capacity of approximately 2 litres and        is provided with a jacket with cooling-water connection.        Planetary drive and dissolver drive are independent. There must        be a vacuum pump present. An additional drum press makes product        transfer easier. Disassembly for cleaning purposes should be        rapid.

c) Formulation

-   -   62.4% silicone polymer    -   Silopren E 50 (GE Bayer Silicones)    -   24.6% silicone oil    -   Silicone oil M 1000 (GE Bayer Silicones)    -   4.0% acetate crosslinker    -   Crosslinker AC 3034 (GE Bayer Silicones)    -   1.0% adhesion promoter    -   Adhesion promoter AC 3001 (GE Bayer Silicones)    -   0.01% dibutyltin diacetate catalyst    -   8.0% fumed silica    -   AEROSIL® (Degussa AG)

d) Procedure

-   -   468.0 g of silicone polymer, 184.5 g of silicone oil, 30.0 g of        crosslinker, 7.5 g of adhesion promoter are weighed out into the        stirring vessel and homogenized for 1 minute with a planetary        drive speed of 50 rev min⁻¹ and a dissolver speed of 500 rev        min⁻¹.    -   Thereafter 60 g of silica are incorporated at the same speed in        2 lots (each about 30 g) and the time required for wetting is        measured.

As soon as the silica is fully wetted, a reduced pressure ofapproximately 200 mbar is applied and dispersion is carried out for 5minutes with the planetary stirrer at 100 rev min⁻¹ and the dissolverdrive at 2000 rev min⁻¹.

A drum press is used to transfer the sealant into two aluminium tubes.

The silicone rubber compound obtained in this way is coated out using adoctor blade and vulcanized at room temperature in ambient air within 24h. The surface of the vulcanizates is assessed visually and rated inaccordance with a school grade system:

Grades: 1=very good, 2=good, 3=satisfactory, 4=unsatisfactory,5=deficient

When the silicas from Examples 1, 3, 4, 6, 7 and 9 are used,surprisingly, good surface properties of the silicone vulcanizates areobtained, in comparison to standard material, despite the fact thatthese silicas in some cases have very high tamped densities, which wouldnormally lead to a poor surface quality. The surface of the siliconevulcanizate with the standard material is no more than satisfactory.

TABLE 6 Properties of non-crosslinked sealants Product Yield Viscositysilica Grinding poing D = 10 s⁻¹ Dispersing Surface Ex. of Bagging [Pa][Pa * s] [grades] [grades] Ex. Comp. Reference 176 85 1.5 3 13 Ex. Ex.Example 1 AJ 184 86 1.5 2 14 No Ex. Example 3 AJ 173 87 1.5 2 15 CarterEx. Example 4 AJ 180 88 1.5 2 16 No Ex. Example 6 AJ 165 84 1.5 2 17Carter Ex. Example 7 PD 163 83 1.5 2 18 No Ex. Example 9 PD 172 86 1.5 219 Carter Grades: 1 = very good, 2 = good, 3 = satisfactory, 4 =unsatisfactory, 5 = deficient

1. Fumed silanized silica having the following physiochemical data:Grindometer value less than 20 μm, and Tamped density 25 to 85 g/l.


2. A process for preparing the fumed silanized silica according to claim1, comprising silanizing a fumed silica having a BET surface area of130±M²/g and then grinding the silanized fumed silica to form groundnon-reagglomerating silanized fumed silica.
 3. Silicon rubber containingas a filler the fumed silanized silica according to claim
 1. 4. Siliconerubber compounds containing 0.5% to 60% by weight of the fumed silanizedsilica having the following characteristic physicochemical data:Grindometer value less than 20 μm, Tamped density 25 to 85 g/l,

and 40% to 99.5% by weight, based on the total mass, of anorganopoly-siloxane of the formulaZnSiR3-n-0-[SiR20]x-SiR3-n-Z′n, where R=alkenyl, alkoxy, aryl, oxime,acetoxy, alkyl radicals, having 1 to 50 carbon atoms, unsubstituted orsubstituted by O, S, F, Cl, Br, I, in each case identical or different,and/or polystyrene, polyvinyl acetate, polyacrylate, polymethacrylateand polyacrylonitrile radicals having 40-10 000 repeater units, Z=OH,Cl, Br, acetoxy, amino, amineoxy, oxime, alkoxyamido, alkenyloxy,acryloxy or phosphate radicals, where the organic radicals contain up to20 carbon atoms, and in each case identical or different, whereZ′=oxime, alkoxy, acetoxy, amino, amido, n=1-3, and x=100-15 000.